Surface texture, mineralogy and stable isotope studies of nodular calcretes preserved in the YTT ash of Padang Terap river basin and Lenggong valley, Peninsular Malaysia: implications in its origin and paleoclimatic reconstruction

Abstract Rounded to sub-rounded calcrete nodules, preserved in Youngest Toba Tuff (YTT, ∼75 ka) ash, exposed at the Padang Terap river basin and Lenggong valley of Malaysia, have been investigated for their micromorphological details, mineralogy and stable isotope compositions (δ18O and δ13C) with the aim to interpret their origin, climatic conditions and vegetational scenario in the studied areas. These nodules are associated with cylindrical, pipe-like, root calcretes and highly calcretized ant traces. The SEM study shows dominance of sparry calcite and microsparite as groundmasses and presence of bacteria microfossils and microbial features. The microfossils are represented mainly by microcodium, calcified pedostructures and organic filaments, whereas, the microbial features as extracellular polymers substances (EPS) and bacillus type bacteria. Mineralogical compositions as reflected by X-ray diffractograms show dominant peaks of calcite across the graphs followed by quartz, chlorite, illite and palygorskite. Stable isotope data suggest that the precipitation of calcium carbonate might have happened in in-situ manner that leached under the influence of meteoric water as well C4 vegetation during the formations of the nodules. Presence of C4 vegetation in the area suggests that the same had revived after the YTT event. The study suggests that the CaCO3 would have been supplied to the host sediments by dust, rainwater and local geological set-ups during arid, semi-arid and humid climatic conditions.